Depends that can be big for them. But mine will get big as a #2 Pencin if I feed them right. What I do is sprinkle Cornmeal over the bed. Just dust the top, them sprinkle it down with water. Cover that up with news paper. Wetting the feed and covering it, causes them to feed more. Thus get bigger as they eat more when the feed is damp. But don't let it get wet if you have thick spots with the feed.
I let mine die out 2 weeks ago. In one containers with 12 gallons of bedding in each. I guess there was a few Thousand in each one. Or more like 5000+ in each. My back did not let me get down to the basement for a week. So they went into survival mode, laying eggs like crazy. Will clean the beds up next week, put the bedding in fresh. Start back watering and feeding these 2 beds, there full of pods or eggs. And after a few weeks they will both be solid worms again. Split them up and make 4 beds..
Again Wigglers will for the most part be just big enough for that #6 hook. But damp cornmeal will fatten the suckers up fast. Old Cotton gin by the school I went to in the early 70's. When they closed down the mill at night, for some reason where all that dust from the cotton seed blowed out on the ground. They wet it down and us boys would go the next am and get worms by the gallons. But only fat big worms if they dampened the stuff down. If it was left dry they did not like it near as much. And the worms were more like strands of hair.
Pete